Production of hydrocarbons used as fuel or heavy oil components and chemicals from biomass are of increasing interest since they are produced from a sustainable source of organic compounds.
The ketoacid Levulinic acid (LA, 4-oxopentanoic acid) is one of many platform molecules that may be derived from biomass. It may be produced from both pentoses and hexoses of lignocellulosic material (see FIG. 1) at relatively low cost. Some of the advantages and drawbacks of using levulinic acid as a platform molecule relates to the fact that it is considered to be a reactive molecule due to both its keto and acid functionality.
Esters of levulinic acid have been suggested as fuel components as well as cold flow additives in diesel fuels, and in particular the methyl and ethyl esters have been used as additives in diesel fuel. Gamma-valerolactone (GVL), which may be obtained by reduction of levulinic acid, has been used as a fuel additive in gasoline. Further reduction of GVL to 2-methyltetrahydrofuran (MTHF) provides a product that may be blended with gasoline of up to 60%. Alkyl valerates produced from levulinic acid have also been suggested as biofuels.
Levulinic acid has also been used for the production of liquid hydrocarbon fuels by a number of catalytic routes, including a method of producing a distribution of alkenes, the distribution centered around C12, involving converting aqueous GVL in a first reactor system to butenes followed by oligomerization in a second reactor over an acidic catalyst (for example, Amberlyst® 70).
Serrano-Ruiz et al. (Appl. Catal., B, 2010, 100, 184) produced a C9-ketone (5-nonanone) by reducing levulinic acid to GVL over a Ru/C catalyst in one reactor followed by reacting 40 wt % GVL in water and 0.02 M H2SO4 in a Pd/Nb2O5+ceria-zirconia double bed arrangement at 325-425° C., 14 bar, WHSV=0.8-0.5 h−1 in another reactor. Using multiple reactors may be advantageous as it can offer more control over the process compared to using a single reactor. However, multiple reactors increase the number of process steps, which is not desired.
US 2006/0135793 A1 (to Blessing and Petrus) discloses dimerization of levulinic acid to a C10 unit in the presence of hydrogen, with a strong acidic heterogenous catalyst comprising a hydrogenating metal, at a temperature in the range from 60 to 170° C. and a pressure of 1 to 200 bar (absolute). The example indicates as main products levulinic acid dimers (26%) and unreacted levulinic acid (70%). Using a single reactor compared to multiple reactors may be advantageous in that it can reduce the number of process steps. Some of the drawbacks associated with direct routes of upgrading, for example, by using single reactors are that these reactions generate highly reactive intermediates with more than one functional group, which can further react to other (unwanted) molecules. Reduction of unwanted molecules by direct routes of upgrading in, for example, a single reactor usually entails a lower yield of the desired product composition. Accordingly, an indirect route of upgrading a feedstock using multiple reactors or multiple catalyst beds in a single reactor may in some situations be preferred compared to a direct route of upgrading.
Consequently, there is a need for additional processes for upgrading levulinic acid and other ketoacids to higher molecular weight compounds, which are suitable for use as, for example, fuel or heavy oil components or chemicals or as components in the production of fuel or heavy oil components or chemicals. For example, there is a need for such additional processes which reduce the processing costs by, for example, improving the yield of the desired components or chemicals and/or improving the life time of the catalyst.